Measurement of interaction between antiprotons

TL;DR

This paper reports the first direct measurement of the attractive nuclear force between antiprotons, providing key parameters that enhance understanding of antinucleon interactions and the structure of antinuclei.

Contribution

The study provides the first direct measurement of the antiproton-antiproton interaction, including scattering length and effective range, using data from the STAR experiment.

Findings

The force between two antiprotons is attractive.

Measured scattering length (f0) and effective range (d0) for antiproton interactions.

Provides fundamental parameters for understanding antinucleon interactions.

Abstract

One of the primary goals of nuclear physics is to understand the force between nucleons, which is a necessary step for understanding the structure of nuclei and how nuclei interact with each other. Rutherford discovered the atomic nucleus in 1911, and the large body of knowledge about the nuclear force since acquired was derived from studies made on nucleons or nuclei. Although antinuclei up to antihelium-4 have been discovered and their masses measured, we have no direct knowledge of the nuclear force between antinucleons. Here, we study antiproton pair correlations among data taken by the STAR experiment at the Relativistic Heavy Ion Collider and show that the force between two antiprotons is attractive. In addition, we report two key parameters that characterize the corresponding strong interaction: namely, the scattering length (f0) and effective range (d0). As direct information on the interaction between two antiprotons, one of the simplest systems of antinucleons, our result provides a fundamental ingredient for understanding the structure of more complex antinuclei and their properties.